It was a conversation John Hancock will never forget. He'd just turned 16 and was studying at the prestigious Phillips Academy in Andover, Boston, when an urgent call came through to drop everything and fly back from the US to Perth, as his grandfather, iron-ore magnate Lang Hancock, wanted to see him.

We want to see our grandfather’s wishes honoured. Lang Hancock did not want Gina to have everything or for her to dictate our lives.

It was a cold and blustery day in the spring of 1992 when Hancock flew out of Boston to begin the 32-hour trip he'd made numerous times before, first to pass tests and interviews, then to attend the school whose roll call of illustrious alumni include actor Humphrey Bogart and presidents George Bush senior and junior. However, never before had he been summonsed home by his grandfather.

Come fly with me … John Hancock with his grandfather, Lang, on Lang’s jet in 1978. Photo: courtesy of John Hancock

Years earlier, in 1985, Hancock's mother, Gina Rinehart, had moved the family to Texas. She did so after a monumental falling out with her father over his controversial marriage to Rose Porteous - and the millions of dollars he lavished on his young wife in the form of a jet, cars, parties, travel, glitzy jewellery and the palatial Prix d'Amour mansion in Perth's Mosman Park that had been modelled on Gone With The Wind's Tara.

Arriving in Perth, Hancock was shocked by the shrunken appearance of the man he saw lying in bed. "He looked much weaker than I'd ever seen him," he says of his then 82-year-old grandfather, who was battling kidney, heart and lung complications. "He'd lost a lot of weight. He took my hand and said, 'You've got to be strong as you will need to run everything one day.'

"He noted my Phillips Varsity Swimming jacket and I said I was thinking of adding my nickname, JR [John Rinehart], to the sleeve and he suggested 'Iron Man' instead. I was chuffed, as I knew he was making a play on the title of a documentary about him, Man of Iron." (The 1966 BBC production had recounted Lang Hancock's discovery in 1952 of the world's biggest iron-ore deposit in the desolate Pilbara region in the north of Western Australia.)

It was a seminal moment for John Hancock. His grandfather's words reinforced his boyhood dream that he would one day run the family empire, Hancock Prospecting, the iron-ore business founded by Lang and which is today managed by his famous daughter, Gina Rinehart.

Just a few hours later, Lang was dead - of multiple organ failure. Hancock remembers waking up the next morning in a guesthouse at Prix d'Amour amid a commotion caused by police and sniffer dogs swarming all over the house, after an anonymous tip that Lang had been murdered. Almost a decade later, an inquest was called after a witness came forward saying he had overheard a conversation that a hit man had been hired to kill Lang.

The magnate was no more, yet the bitter controversies and litigation that had dogged his final years would continue, incredibly, for another three decades. They will culminate in a legal showdown between Gina Rinehart on one side, and on the other, Bianca Rinehart, the first of her three daughters, and John Hancock, her eldest child and only son, on October 1.

Forged in iron … John aged 21 at the Sishen Iron Ore Mine in South Africa. Photo: courtesy of John Hancock

A dying man's vision for Hancock Prospecting remains Hancock's driving force in the current legal battle over the family trust. "From the start I've said we are doing this to carry out the intentions of my grandfather, and for fairness to everyone," he tells me.

The current action was launched on September 5, 2011, by Rinehart's third child, Hope Welker, now 28, over the multi-billion-dollar Hope Margaret Hancock Trust that Rinehart has been running on behalf of her four children since 1992. A few days later, Hope's two older half-siblings, Hancock, now 37, and Bianca Rinehart, 36, joined the action to have their mother removed as trustee, claiming "deceptive, manipulative and disgraceful conduct" in relation to her management of the trust.

Twenty-seven-year-old Ginia Rinehart, Rinehart's youngest daughter and the child who is said to most resemble her mother, chose not to join her siblings in the action. Earlier this year, Hope withdrew due to financial pressures and a marriage breakdown, leaving John and Bianca as plaintiffs.

Happier times … Gina Rinehart with son John and daughter Ginia in Melbourne in 2009.

The trust, which owns almost 25 per cent of Hancock Prospecting, was set up in 1988 by Lang Hancock for the benefit of Rinehart's four children to pay for their "education, advancement and benefit". Once Ginia turned 25, on September 6, 2011, it stated, it would vest, giving each of them financial independence.

The stakes are high. The trust is worth at least $5 billion, based on BRW magazine estimates, which would make each of the children billionaires in their own right. But the reality is they've had little access to their inheritance since Rinehart took over from Lang as trustee when the children were minors. Put simply, it has been a case of "Mother knows best". John and Bianca allege that she is purposely keeping them in the dark about what is going on in the business to keep them under her thumb.

Their key claim revolves around Rinehart's decision as trustee to demand the voting rights to the children's shares in return for extending the vesting date of the trust from September 6, 2011, to 2068 - when they will be in their dotage - otherwise they'd be bankrupted by a massive capital gains tax bill. She informed them in a letter they had three days to agree to the plan. Less than a year later, John Hancock obtained a ruling from the Australian Tax Office that said there would be no capital gains tax on vesting. This means no bankruptcy threat.

More significantly still, it was also Lang's intention, stated just before he died, that John and Bianca control the lucrative Hope Downs tenements, which currently generate about $1 billion a year, through the family trust. After his death, these tenements were transferred to Hancock Prospecting, which is majority owned by Rinehart. ("Tenement" refers to the pegging of land to make a legal claim on it with the purpose of exploring and building a mine. Hope Downs was the name given to a piece of the Pilbara that was pegged by Lang Hancock and is the jewel in the company crown.)

Asked what outcome he wants to see from the impending trial, Hancock says unequivocally: "We want to see our grandfather's wishes honoured. He did not want Gina to have everything or for her to dictate our lives. My grandfather would be greatly troubled. He did not want his discoveries and life's work to be a source of problems, but rather a great start and foundation for us, his grandchildren, in the way his work supported my mother in her early years. He was generous and gave her a third of his company shortly after she was born - it was always the family company. He'd be furious Hancock Prospecting staff have involved themselves with these matters, and so am I, quite frankly."

For her part, Rinehart believes her warring children are "manifestly unsuited" to running the trust. Documents filed in the court state that none of the plaintiffs has "the requisite capacity or skill or the knowledge, experience, judgement or responsible work ethic" to manage it. "Given the media attention, attacks on the rich by the Treasurer, the impending breach of Australia's loan covenants and need for extra revenue, it is also now time to bring this dispute privately under arbitration," she wrote soon after the legal action began.

Hancock remains unfazed by this latest battle with his mother, a woman whom veteran lawyer Nick Styant-Browne describes as "an indefatigable litigant with almost limitless resources" and "one of the most experienced litigators in Australian legal history".

Alan Camp, who as a young law student was taken under Lang Hancock's wing and who has known the family for more than 40 years, describes John as a battler, too. "He will fight for what his grandfather wanted," he says. "He has no choice. He is fighting for his family. His own and his mother's."

The stoush has captured the imagination of the world as Rinehart, one of the richest women on the planet, takes on two of her four children. Rinehart holds just over 75 per cent of Hancock Prospecting, which puts her in an all-powerful position when it comes to controlling the family's purse strings. Since she began managing the trust, the family fortune has ballooned from tens of millions of dollars, according to BRW, to an estimated value of $22 billion.

Beyond money, however, the fight is about power, control and an absolute breakdown of trust between the family members. Nick Styant-Browne, who opposed Rinehart in an action she brought against her stepmother, says she wants "control of her father's estate, control of the trusts which her father established, even control of the media. Her recent foray into Fairfax Media [publisher of Good Weekend] reflects her desire to take a more proactive media position."

Mark C. Williams, professor of applied positive psychology at Shenzhen University in China, has been following the case for the past two years and questions Rinehart's motivations. "She could be just wanting to maintain total control," he says. "Or she could be testing the mettle of her children - their mental and emotional strengths, in an almost Darwinian way - to determine the outcome of what one hopes might be a succession plan. Might a better approach be to encourage their unique strengths in independent spheres of influence, and thus find positive outlet for their energies?"

Three of Rinehart's children have already made her a grandmother. Hancock has two young daughters, who are 4 and 6, with Gemma, who has been by his side for 12 years. Bianca has a three-year-old son with her partner, the Moscow-born Sasha Serebryakov, while Hope, now separated from her American husband, Ryan Welker, also has two young daughters, who are 5 and 8. Ginia is engaged to Ryan Johnston, the son of one-time Beach Boy Bruce Johnston.

Greg Milton, the Englishman who was married to Rinehart for eight years from 1973 to 1981 and is the father of John and Bianca, sees the case as a fight being undertaken by an organisation that "appears to be continuing a vendetta against [his] children for no valid reason except [their] mother may have something personal against me or want roles and privileges for her second set of children [Hope and Ginia, fathered by Frank Rinehart] to the detriment [of John and Bianca]. It's amazing John can withstand that sort of pressure."

When Milton and Rinehart divorced in 1981, he received a $60,000 settlement and agreed he wouldn't see John and Bianca, who were 4 and 5 at the time, until they were adults. He now lives in Indonesia and, until now, has been reluctant to comment publicly on his ex-wife. "I am personally disgusted that my children are now having to fight the Office Machine [a term he uses to describe the entourage of lawyers and accountants who do Rinehart's bidding], as I had to, to receive what Lang intended them to have as a matter of course."

Hancock declines to comment on the motivations of his mother, except to say that he remembers her, as a young mother in her 20s, as caring, happy and elegant. "Bianca and I have great memories of our three-person family in the Pilbara and other travels together," he says. "But she changed after she married Frank."

His reluctance to say too much is partly driven by a deed his mother asked him to sign in 2007, known as the Hope Downs Deed, that prevents him and his siblings from saying anything publicly that might embarrass their mother. Indeed, Rinehart's insistence on privacy runs so deep that she spent months in court fighting to keep the details of the current case suppressed. Her argument was rejected and when the suppression order was finally lifted on March 9, 2012, journalists had a field day pouring over the contents of personal emails that had been exchanged between various members of this warring clan.

What became all too apparent is that money really can't buy happiness. Nor should it be used to turn the courts into a personal playground, provided at the public's expense, argued Jim McGinty, who was appointed West Australian Attorney-General in 2002, just 10 weeks before the verdict was delivered at the inquest into Lang Hancock's death. At the time, McGinty expressed sadness at the way the law had been misused in a personal squabble between Porteous and Rinehart, thereby squandering valuable resources and holding up other inquests.

The inquest, sought by Rinehart to investigate Lang's death because she didn't believe he'd died of natural causes, quickly degenerated into a circus. In the end, though, the coroner found that the old man had died of natural causes, which were consistent with the findings of the original autopsy.

The October 1 trial won't be as colourful as the inquest, but it promises to be a bloody affair. In one corner is heavyweight Rinehart, backed by a retinue of expensive lawyers and limitless cash; in the other, John and Bianca, now forced to rely on the skill of one lawyer after being cut off from family money.

And Rinehart learnt from the best. Her second husband, Frank Rinehart, was 37 years her senior and a man her father couldn't stand when she married him in 1983. He was also a ruthless American corporate lawyer who'd been convicted of tax fraud, a fact she successfully kept hidden from her children until the publication, last year, of Gina Rinehart: The Untold Story Of The Richest Woman In The World, by this author.

Lang, noting the changes he saw taking place in his daughter after her second marriage, famously remarked in a letter to her: "At least allow me to remember you as the neat, trim, capable and attractive young lady of the 'Wake Up Australia' tour [when she was married to Greg Milton], rather than the slothful, vindictive and devious baby elephant that you have become. I am glad your mother cannot see you now."

After Lang's death, Rinehart took aim at Porteous in an attempt to seize back more than $30 million-worth of assets, including the Prix d'Amour mansion, alleging the gifts had been paid for with family money.

After more than a decade of litigation, matters were settled in 2003, with Porteous retaining many of the gifts lavished on her by Lang. Now 65, she lives in Perth as a beauty therapist, according to online magazine, The Starfish.

A woman of seeming inexhaustible appetite for battle, Rinehart has also taken on the family of her father's business partner, Peter Wright, and other mining companies, including BHP and Rio Tinto.

When Frank died intestate in March 1990, Rinehart discovered he'd had a long-term mistress during his four-decades-long marriage to his first wife, Elizabeth Campbell, with whom he had three sons. It seemed that when he wasn't living with Elizabeth and the boys in Massachusetts, he shared a spacious Fifth Avenue apartment in New York with Lorraine Boyce and her children. Boyce was in her 70s when she learnt in a letter that Rinehart wanted the apartment she'd been living in for the past 26 years. She spent more than eight years entangled in legal action with her dead lover's second wife until she died in 2001. The case was settled, but the details aren't known.

Rinehart's latest stoush with her children is her most personal cause to date. To outsiders, the action came as a shock; to those in the know, it seemed almost overdue. To understand the depth of the family division requires a step or two back in time to a point where the relationship between the four children was forged by the impact that their different fathers had on their upbringing.

For some onlookers, the different paternities of the two sets of children is key to understanding the twists and turns of the family saga. Rinehart placed Frank, the hot-shot lawyer and Harvard graduate, on a pedestal throughout their short, but dedicated marriage; Greg Milton, on the other hand, she came to think of as a mistake of her youth and she couldn't airbrush him from her memory fast enough.

John Hancock himself asserts that because of the perceived "genetic superiority" of Hope and Ginia, they have always been treated better by their mother than himself and Bianca. He believes that because he didn't graduate from Harvard Law School like his stepfather (he did an MBA at Notre Dame University), his mother views him as somehow unworthy. "Ginia didn't graduate from Harvard, either," he says, "but the girls, especially Frank's, are treated differently."

The children were brought up in an atmosphere of swirling aggression. First, there was the protracted fighting between their mother and their grandfather after he married Porteous; then litigation between their mother and Boyce; and, finally, more bitter litigation between Rinehart and Porteous. They lived with constant reminders that their wealth had made them a target.

It was a conspiratorial world, according to Michael Yabsley, a former consultant to Hancock Prospecting who has known Rinehart since she was a teenager. "Conspiracies, paranoia - these are very significant parts of her life," he says. "There's a total lack of trust, which I think is evidenced by her staff turnover."

In a rare interview given last October, Bianca told Vogue that she lived in fear as a little girl of being kidnapped: "With tour buses stopping in the front of your house ... it does make you feel exposed. I was concerned at times - I actually used to sleep with a hammer under my mattress."

Frank's treatment of the children varied according to their gender. "What today would be considered physical and emotional abuse, 60 years ago was considered a 'toughening-up' process for boys," says Hancock now.

"When [Frank] got angry, it built like a steam engine gaining pressure," he revealed in his mother's biography. "You could see it: a vein on the side of his neck would pump. The eyes were the most scary. He was a strong man in his time and even then. I saw him stand up to men half his age without an ounce of fear several times - with cause or without - usually with my mum in the background saying, 'Oh Frank, please don't'. "

A relative of Frank's, speaking anonymously, tells me how he destroyed the lives of two of his three sons from his first marriage. The eldest son became estranged from the family in the '70s, while the youngest died of cirrhosis of the liver at 29. "Frank was a bully," he says. "If your view of the world was not like his, you were wrong and he beat you to a pulp - verbally most of the time ... In some cases, it actually became physical. He had this picture of what his family should look like and would not accept another scenario. He had a need to stand out, to be noticed, to be in charge."

In the biography, Hancock recalls a shocking incident when he was 12. The family was in the middle of a three-day road trip from Perth to Broome when, John, bored, started to misbehave. Rinehart pulled over and asked Frank to discipline him. "So he opened the rear window to the Range Rover, cocked his fist and punched me in the head," says Hancock. "I had neither the room nor the time to do anything. Blood flowed from my lip. He let me out of the car and took me to the petrol station toilets and cleaned me up. I refused to give him the satisfaction of crying, but it was pretty shocking; it all happened so quickly. As we left the highway, I saw a police car. I was so tempted to make a run for it."

Each of the siblings has, at some stage, watched the others be handpicked for succession by their mother, only to be discarded. In 1997, Hancock was appointed director of Hancock Prospecting and represented the company at conferences in Asia and Europe; he worked in iron-ore mines and steel works in South Africa. But, in 2003, when his mother settled with Porteous, he was no longer required in the business. (A disagreement between mother and son about their lawyers was enough for her to stop his salary.) He quietly changed his name from Rinehart to Hancock and challenged her role as trustee of the family trust.

In May 2004, his lawyers wrote to Rinehart saying, "There has been a failure on your part to distinguish between the interests of the various entities you control and the interests of the trust." The letter revealed that "mining interests had been transferred out of the trust". In another letter, he says he believed his grandfather intended for the family trust to hold 49 per cent of Hancock Prospecting as well as "certain mining interests". The four children today hold less than 25 per cent of Hancock Prospecting through the trust, due to a debt reconstruction undertaken in 1995 after Lang died.

When John failed to gain financial support from the trust, he withdrew from the legal action in 2007, agreeing to "forever abandon" his allegations and, in return for a salary and his reappointment to the executive committee (until then, he had received nothing from the trust since the falling out with his mother, while his sisters continued to receive trust payments), forgo any legal claims against his mother, Hancock Prospecting and the trust. (The High Court has ruled that the current action lies outside the deed.) He signed the Hope Downs Deed and waited for September 6, 2011, the day when the trust would vest and he would finally be granted his freedom - or so he thought.

Bianca has also been sidelined. In 2004, at the age of 27, she became a secretary and government relations adviser in the company after completing a hospitality/hotel management degree in Adelaide. By June 2008, though, she had resigned from several company boards and withdrawn from full-time employment, citing personal reasons. Friends say she wasn't being given sufficient responsibility and didn't have enough work to do.

Having already alienated John, Rinehart had now ostracised her eldest daughter, too. Where Lang had devolved power and responsibility upon Rinehart before their falling out, she clearly was incapable of doing the same.

Hope's husband, Ryan Welker, a consultant for Hancock Prospecting in Sydney, was the next to spin the wheel of succession. Hope, who never had any ambitions to enter the family business, had married the former model in 2005 when she was just 19. But Welker also ran into difficulties working with his mother-in-law and when he advised Hope she should challenge her mother over the family trust in September 2011, his journey at Hancock Prospecting came to an abrupt end.

Whether by accident or design, Ginia, the youngest, is now the anointed one. She is most like Rinehart in her ways and was always her mother's favourite and the most indulged. Like Hope, she enjoyed a privileged childhood, spending most of it overseas at one of the best schools money can buy, Le Rosey in Switzerland, and holidaying in the Mediterranean with helicopters on tap.

Until recently, she showed little interest in the iron-ore business. She completed a degree in business, majoring in Spanish, in London in 2010 and took a job at Fabergé. People who know Ginia say she's more at home sitting in the front row of fashion parades than spending time in the Pilbara, but after the legal action began, pictures began to appear of her dangling the key to a $1.2 million Rolls-Royce Phantom from her finger.

The release of personal emails after the lifting of the suppression order in March last year - including ones from Hope to her mother, written in July 2011, asking for funds to hire a chef, bodyguard and housekeeper - didn't paint a flattering picture. A press release, issued by Ginia within minutes of the emails' release, decrying the legal action of her siblings as "motivated by greed", didn't help.

But Hancock insists the emails were taken out of context. Rinehart wanted Hope to leave New York, where Welker was trying to secure mining consulting work, and move to Singapore. "Hope didn't want to go to Singapore," he explains, "because she was trying to build a new life for herself in the US. She knew GHR [Gina Hope Rinehart] wouldn't provide funds for these things, which gave her the excuse she was looking for not to go. The only person in our family who enjoyed that kind of lifestyle was our mother."

Sitting at Italian restaurant Il Lido in Perth's beachside suburb of Cottesloe, eating lunch with Gemma and a few friends, Hancock seems to be in complete control. In less than a month from now, though, he will take the stand in the NSW Supreme Court and face what promises to be a serious grilling by his mother's lawyers - unless the pair can reach a settlement.

Lawyer Alan Camp, who knows the clan well, says Hancock is very much like his grandfather in temperament and engaging sense of humour. "In the end, when all this litigation is over, John will put it all behind him and work out and reconcile his relationship with his mother," he says. "That's the man he is.

"He only wants to work with his mother. He shares his grandfather's vision of a successful family company and a better Australia. He doesn't want a nightmare. He is a strong and emotionally mature young man. He sees no future in disharmony, as I'm sure Gina doesn't, either."

Legal experts point out that, in cases of family feuds like this one, settlements are often brokered at the doors of the court. Rinehart has said she's open to the idea, but the sticking point will be the terms of agreement.

"It will soon become evident if the bond that exists between all members of the Hancock family can overcome this generational turmoil," says Professor Mark C. Williams. "I see a lot of love, despite the exterior appearance of brutality. But maybe I'm wrong."

Whatever the case, John Hancock is ready for the fight. He says that once he received the September 3, 2011, letter from his mother asking the children to extend the trust or they could face bankruptcy, he offered to stay out of everything for $25 million. "Then Bianca called me and asked for my support in the legal action Hope wanted to commence in Sydney. I asked if all the siblings, including Ginia, were on board and the answer was yes," he says. (Ginia had originally said she would join the action, but backed out after talking to her mother about the threat of bankruptcy.)

At the time, Hancock was a member of the executive committee of Hancock Prospecting, a role he'd been given in 2007 after reaching the truce with his mother. He'd also started discussions with Hancock Prospecting's chief financial officer, Jay Newby, about setting up an independent investment vehicle, financed by the company, and run by him.

But, in the end, he decided to back the girls. "I smelt a rat," he says when he received a letter from Newby on the eve of the trust vesting. "I did not believe Jay and I argued with him about the supposed capital gains tax bill for the next few days. It was high stakes for me, but I'd been in situations like this before with them [senior executives who work for Hancock Prospecting]. I called their bluff and didn't sign."

The decision to launch a legal action against Rinehart wasn't taken lightly by the siblings. Bianca was forced to sell her house, Hope to liquidate assets, including selling clothes on eBay, while John had to manage a demanding job in Perth as CEO of building products company FBM while simultaneously organising funding to bankroll the case.

"I brought a consortium of friends and business colleagues together - some interest-free - and raised $1 million with a 50 per cent per annum rate [the source of the loan funds is confidential]," says John. "My intention from the start was to let the girls run the show. I'd already done several rounds with my mother in 2005."

In January, Hope, the mother of two young children with a broken marriage behind her, withdrew from the lawsuit in return for a settlement. In an email to Ginia, sent on November 22, 2011, she said, "I'm in a corner [with] a gun at my head. I can't afford rent, I can't afford the kids' education, I don't know what else to do or who else to ask. Please help."

Ginia's response was as follows: ''I actually didn't think it was possible for you to stoop any lower, but voila you proved me wrong again. Not that you deserve a penny as you have never worked a day in your life but, if you cannot live with 300 million dollars for doing absolutely nothing, then you really are disgusting. Stop being such a shit parent to the most awesome little girls, her and I [sic] both deserve better from you! SHAPE UP!"

Whether Hope received a $300 million settlement is anybody's guess. Her brother believes she's unlikely to be receiving much more than basic living expenses and little or nothing upfront. Meanwhile, the relationship between the two younger sisters remains strained. Hope visited her mother over Easter and sailed around Perth, but got off the yacht as Ginia boarded it.

Meanwhile, Rinehart's lawyers are pitching the coming court case as mother versus son. "He [John] may be in the evidence box for some time," says one, suggesting "with some certainty" that Rinehart will, ultimately, be the victor. Her defence, he adds, will comprise evidence that is "extensive" and "not very pleasant".

Twenty-one years after Lang Hancock told his 16-year-old grandson to prepare to take the helm of the family company, John Hancock is undeterred by the fight ahead, his eyes still firmly on the prize.

"I won't give up and my mother should know that even the five top QCs she has ready to cross-examine me at a seven-day trial will be a walk in the park compared to an intense hour with Frank," he says. "My hope is my mother is just doing this to apply the blowtorch and see what my melting point is."

Stay tuned.

Lead-in photograph courtesy of John Hancock.

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